Fix #8758 (graduated classes on expression broken)

wonder-sk · wonder-sk · commit a64610186173 · 2014-02-12T19:52:00.000+07:00
diff --git a/src/core/symbology-ng/qgsgraduatedsymbolrendererv2.cpp b/src/core/symbology-ng/qgsgraduatedsymbolrendererv2.cpp
@@ -641,6 +641,9 @@ static QList<double> _calcJenksBreaks( QList<double> values, int classes,
   // Returns class breaks such that classes are internally homogeneous while
   // assuring heterogeneity among classes.
 
+  if ( !values.count() )
+    return QList<double>();
+
   if ( classes <= 1 )
   {
     return QList<double>() << maximum;
@@ -772,15 +775,22 @@ QgsGraduatedSymbolRendererV2* QgsGraduatedSymbolRendererV2::createRenderer(
   int attrNum = vlayer->fieldNameIndex( attrName );
   double minimum;
   double maximum;
+
+  QScopedPointer<QgsExpression> expression;
+
   if ( attrNum == -1 )
   {
+    // try to use expression
+    expression.reset( new QgsExpression( attrName ) );
+    if ( expression->hasParserError() || !expression->prepare( vlayer->pendingFields() ) )
+      return 0; // should have a means to report errors
+
     QList<double> values;
     QgsFeatureIterator fit = vlayer->getFeatures();
     QgsFeature feature;
-    QgsExpression expression( attrName );
     while ( fit.nextFeature( feature ) )
     {
-      values << expression.evaluate( feature ).toDouble();
+      values << expression->evaluate( feature ).toDouble();
     }
     qSort( values );
     minimum = values.first();
@@ -808,15 +818,21 @@ QgsGraduatedSymbolRendererV2* QgsGraduatedSymbolRendererV2::createRenderer(
     // get values from layer
     QList<double> values;
     QgsFeature f;
-    QgsAttributeList lst;
-    lst.append( attrNum );
+    QStringList lst;
+    if ( expression.isNull() )
+      lst.append( attrName );
+    else
+      lst = expression->referencedColumns();
 
-    QgsFeatureIterator fit = vlayer->getFeatures( QgsFeatureRequest().setFlags( QgsFeatureRequest::NoGeometry ).setSubsetOfAttributes( lst ) );
+    QgsFeatureIterator fit = vlayer->getFeatures( QgsFeatureRequest().setFlags( QgsFeatureRequest::NoGeometry ).setSubsetOfAttributes( lst, vlayer->pendingFields() ) );
 
     // create list of non-null attribute values
     while ( fit.nextFeature( f ) )
-      if ( !f.attribute( attrNum ).isNull() )
-        values.append( f.attribute( attrNum ).toDouble() );
+    {
+      QVariant v = expression.isNull() ? f.attribute( attrNum ) : expression->evaluate( f );
+      if ( !v.isNull() )
+        values.append( v.toDouble() );
+    }
 
     // calculate the breaks
     if ( mode == Quantile )
